Size Of Microdomains Research Articles

Preparation of diblock copolymer films for the localization of C60 and multiwalled carbon nanotubes on aqueous substrate

Dropping polystyrene-block-poly(ethylene oxide) (PS-b-PEO) solution on a still and clean water surface caused the formation of homogeneous films of diblock copolymer at the organic vapor/water interface. The morphologies of the PS-b-PEO were studied to control and modulate the arrangement of ordered structures by applying different solvents at different annealing times. After 24 h of annealing under toluene vapor, a lamellar morphology was produced, whereas a cylindrical morphology was produced under chloroform vapor. This simple method was used to obtain more than one type of ordered microdomain structure using the same symmetric diblock copolymer. Interestingly, the microdomain size reached 120 nm, much larger than that obtained by bulk or solution self-assembly. The microphase-separated PS-b-PEO copolymer was utilized as a novel template for the selective self-assembly of the polymer-functionalized C60 and the carbon nanotubes (CNTs) by combining aqueous substrate with solvent annealing. The PS-grafted C60 enhanced the PS-b-PEO to form a lamellar microstructure. The PS-grafted C60 accommodated in the PS phase expanded the scale of PS domains. The PEO-covered CNTs were prepared to form a PEO-covered CNT/water solution for application to a complex substrate with diblock copolymer templates. This methodology enables accommodation of a selective assembly of the CNTs onto the PEO phase. This assembly strategy is a versatile approach and may open a new route for the controlled assembly of anisotropic nanostructured materials with desirable patterns on soft substrate.

Fluctuation-induced forces in critical crosslinked polymer blends

Abstract In this paper, we report on the computation of the induced forces in crosslinked polymer blends, with immersed small colloidal particles (nanoparticles) or confined to two parallel plates (film). We assume that the particles or the walls prefer to be attracted by one polymer, close to the spinodal temperature where a microphase separation takes place. This is the so-called “critical adsorption”. As an assumption, the particle diameter or the film thickness is considered to be small enough in comparison with the size of microdomains (“mesh size”). The critical fluctuations of the crosslinked mixture induce a pair potential between particles located in the non-preferred phase or between the confining walls. The purpose is to recall how this Casimir pair potential can be determined, as a function of the interparticle distance or the walls separation. To achieve calculations, use is made of an extended de Gennes model that takes into account the colloid-polymer and polymer-wall interactions. Finally, the obtained results are compared to those relatively to uncrosslinked polymer blends in the same geometries, and the main conclusion is that the induced force is reduced by the presence of permanent crosslinks.

P09. Cell shape and F-actin regulate Hippo signaling pathway

The proliferation of cultured cells is regulated by cell density, a phenomenon known as cell contact inhibition of proliferation. Previously, we and others have shown that high cell density inactivates the transcription factor Tead, which controls cell proliferation, via the Hippo signaling pathway by suppressing nuclear localization of the coactivator protein Yap. Cell density affects both, cell–cell contacts and the cell shape, but the exact role of these latter cellular properties in regulating the Hippo pathway remains elusive. In this study, we examined the role of the cell shape on the Hippo pathway. To exclude the effects of cell–cell contacts, individual NIH3T3 cells were cultured in small cell–adhesive areas termed microdomains. The cell shape was changed according to the microdomains size. Nuclear localization of Yap was observed with large microdomains or corresponding flattened cells, but not with small microdomains resulting in the formation of round cells. Clear stress fiber formation was observed only in large microdomains concomitant with nuclear Yap. Disruption of F-actin by drug treatment reduced the nuclear localization of Yap and transcriptional activity of Tead irrespective of cell shape. Core components of the Hippo pathway (upstream to downstream) are Merlin, Mst, Lats, Yap and Tead. When activity of the Hippo pathway was blocked by the expression of a dominant negative form of Merlin, Yap stayed in the nucleus, even when F-actin was disrupted. These results suggest that F-actin regulates the Hippo pathway upstream of Merlin, and that the cell shape regulates the Hippo pathway independent of cell–cell contacts by controlling the amount of F-actin.

Casimir Force between Nanoparticles Immersed in a Crosslinked Polymer Blend

We consider a crosslinked polymer blend made of two polymers of different chemical nature. We suppose that such a system incorporates small colloidal particles, which prefer to be attracted by one polymer, close to the spinodal temperature. This is the so-called critical adsorption. As assumption, the particle diameter, d0, is considered to be small enough in comparison with the size of microdomains (mesh size) ξ∗ ∼ an, with a — the monomer size and n — the number of monomers between consecutive crosslinks. The critical fluctuations of the crosslinked polymer mixture induce a pair-potential between particles located in the non-preferred phase. The purpose is the determination of the Casimir pair-potential, U2(r), as a function of the interparticle distance r. To achieve calculations, use is made of an extended de Gennes field theory that takes into account the colloid-polymer interactions. Within the framework of this theory, we first show that the pair-particle is attractive. Second, we find for this potential the exact form: U2(r)/kBT = −AH(d0/r) exp(−r/ξ∗) − BH(d0/r) exp(−2r/ξ∗), with the known universal amplitudes AH > 0 and BH > 0 (the Hamaker constants). This expression clearly shows that the pair-potential differs from its homologue with no crosslinks only by the two exponential factors exp(−r/ξ∗) and exp(−2r/ξ∗). The main conclusion is that the presence of reticulations reduces substantially the Casimir effect in crosslinked polymer blends.

In silico analysis of microdomain-mediated trimer formation in the T cell membrane

We consider stochastic reaction-diffusion dynamics involved in the formation of a trimeric protein receptor complex, where diffusion is modulated by the presence of small, fixed membrane microdomains. Compartmentalisation of cell membrane signalling proteins may optimise signal transduction but previous modelling work suggests that signalling is only augmented if microdomains are highly mobile. Using a Gillespie algorithm-based spatial numerical simulation, we examine the effect of the presence, size and total coverage of microdomains, which either slow protein diffusion or trap proteins at their boundary. We examine scenarios where protein-protein interactions take place within microdomains, and also where interactions are favoured at the microdomain boundary. This model is motivated by the formation of the high-affinity receptor for the cytokine IL-2. Proliferation requires a threshold number of bound receptors, but pleiotropic effects of IL-2 on other cell types means that high ligand concentrations are undesirable. Hence, optimising T cell sensitivity to IL-2 is essential. In agreement with earlier models, we find that small microdomain sizes result in the greatest augmentation in receptor formation, but that static microdomains can also confer an increased sensitivity in the case of heterotrimeric receptor complex formation.

Surface topography of membrane domains

Elucidating origin, composition, size, and lifetime of microdomains in biological membranes remains a major issue for the understanding of cell biology. For lipid domains, the lack of a direct access to the behaviour of samples at the mesoscopic scale has constituted for long a major obstacle to their characterization, even in simple model systems made of immiscible binary mixtures. By its capacity to image soft surfaces with a resolution that extends from the molecular to the microscopic level, in air as well as under liquid, atomic force microscopy (AFM) has filled this gap and has become an inescapable tool in the study of the surface topography of model membrane domains, the first essential step for the understanding of biomembranes organization. In this review we mainly focus on the type of information on lipid microdomains in model systems that only AFM can provide. We will also examine how AFM can contribute to understand data acquired by a variety of other techniques and present recent developments which might open new avenues in model and biomembrane AFM applications.

Magnesium-induced lipid bilayer microdomain reorganizations: implications for membrane fusion.

Interactions between dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylserine (DPPS), combined both as binary lipid bilayer assemblies and separately, under the influence of divalent Mg2+, a membrane bilayer fusogenic agent, are reported. Infrared vibrational spectroscopic analyses of the lipid acyl chain methylene symmetric stretching modes indicate that aggregates of the two phospholipid components exist as domains heterogeneously distributed throughout the binary bilayer system. In the presence of Mg2+, DPPS maintains an ordered orthorhombic subcell gel phase structure through the phase transition temperature, while the DPPC component is only minimally perturbed with respect to the gel to liquid crystalline phase change. The addition of Mg2+ induces a reorganization of the lipid domains in which the gel phase acyl chain planes rearrange from a hexagonal configuration toward a triclinic, parallel chain subcell. Examination of the acyl chain methylene deformation modes at low temperatures allows a determination of DPPS microdomain sizes, which decrease upon the addition of DPPC-d62 in the absence of Mg2+. On adding Mg2+, a uniform DPPS domain size is observed in the binary mixtures. In either the presence or absence of Mg2+, DPPC-d62 aggregates remain in a configuration for which microdomain sizes are not spectroscopically measurable. Analysis of the acyl chain methylene deformation modes for DPPC-d62 in the binary system suggests that clusters of the deuterated lipids are distributed throughout the DPPS matrix. Light scattering and fluorescence measurements indicate that Mg2+ induces both the aggregation and the fusion of the lipid assemblies as a function of the ratio of DPPS to DPPC. The structural reorganizations of the lipid microdomains within the DPPS-DPPC bilayer are interpreted in the context of current concepts regarding lipid bilayer fusion.

Morphology and Deformation Mechanisms and Tensile Properties of Tetrafunctional Multigraft Copolymers

Morphology and deformation mechanisms and tensile properties of tetrafunctional multigraft (MG) polystrene-g-polyisoprene (PS-g-PI) copolymers were investigated dependent on PS volume fraction and number of branch points. The combination of various methods such as TEM, real time synchrotron SAXS, rheo-optical FTIR, and tensile tests provides comprehensive information at different dimension levels. TEM and SAXS studies revealed that the number of branch points has no obvious influence on the microphase-separated morphology of tetrafunction MG copolymers with 16 wt % PS. But for tetrafunctional MG copolymers with 25 wt % PS, the size and integrity of PS microdomains decrease with increasing number of branch point. The deformation mechanisms of MG copolymers are highly related to the morphology. Dependent on the microphase-separated morphology and integrity of the PS phase, the strain-induced orientation of the PS phase is at different size scales. Polarized FT-IR spectra analysis reveals that, for all inves...

Fyn Tyrosine Kinase Regulates the Surface Expression of Glycosylphosphatidylinositol-linked Ephrin via the Modulation of Sphingomyelin Metabolism

Glycosylphosphatidylinositol-linked ephrin-As play important roles in various biological events, such as neuronal development and immune responses. Because the surface amount of ephrin-As is critical in these events, the trafficking of ephrin-As must be regulated by intracellular machinery. In particular, Src family protein-tyrosine kinases regulate the intracellular trafficking of several membrane molecules and act downstream of ephrin-As; whether they affect the trafficking of ephrin-As, however, has remained unexplored. Here, we report that the activity of Src family protein-tyrosine kinases, particularly Fyn, negatively regulates the cell-surface amount of ephrin-As. The expression of constitutively active Fyn decreases the surface amount of ephrin-As. Conversely, the expression of dominant-negative Fyn or the application of a Src-family inhibitor increases the surface amount of ephrin-A2. The total cellular amount of ephrin-A is inversely correlated with its amount on the surface, suggesting that ephrin-As are more stable in the intracellular compartment. The expression of constitutively active Fyn increases the amount of sphingomyelin clusters on the plasma membrane, whereas inhibiting Fyn decreases it. Moreover, the inhibition of sphingomyelin synthesis greatly increases the surface amount of ephrin-As. Altogether, these results suggest that Fyn regulates the surface amount of ephrin-As by modulating the metabolism of sphingomyelin, which presumably inhibits the trafficking of ephrin-As from endosomes to the plasma membrane. The signaling cascade described here may function as part of the negative feedback loop of ephrin-A function.

Lateral Ordering of Cylindrical Microdomains Under Solvent Vapor

The development of the morphology in asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) thin films in tetrahydrofuran (THF) vapor, a selective solvent for majority PS block, as a function of time was investigated by scanning force microscopy (SFM) and grazing incidence small-angle X-ray scattering (GISAXS). When the PS-b-P4VP films were spin-coated from a toluene/THF mixture onto a silicon substrate, cylindrical microdomains were found to be oriented normal to the surface. By annealing under the THF solvent vapor, the distribution of the size and center-to-center distance between the cylindrical microdomains were significantly narrowed. The orientation and grain size of the cylindrical microdomains in the annealed films were characterized using Moiré analysis obtained from SFM scan. GISAXS was used to characterize the morphology of the entire film.

The structure of detergent-resistant membrane vesicles from rat brain cells

The size and the bilayer thickness of detergent-resistant membranes isolated from rat brain neuronal membranes using Triton X-100 or Brij 96 in buffers with or without the cations, K +/Mg 2+ at a temperature of either 4 °C or 37 °C were determined by dynamic light scattering and small-angle neutron scattering. Regardless of the precise conditions used, isolated membrane preparations consisted of vesicles of ∼ 100 to 200 nm diameter as determined by dynamic light scattering methods, equating to an area of the lipid based membrane microdomain size of 200 to 400 nm diameter. By means of small angle neutron scattering it was established that the average thickness of the bilayers of the complete population of detergent-resistant membranes was similar to that of the parental membrane at between 4.6 and 5.0 nm. Detergent-resistant membranes prepared using buffers containing K +/Mg 2+ uniquely formed unilamellar vesicles while membranes prepared in the absence of K +/Mg 2+ formed a mixture of uni- and oligolamellar structures indicating that the arrangement of the membrane differs from that observed in the presence of cations. Furthermore, the detergent-resistant membranes prepared at 37 °C were slightly thicker than those prepared at 4 °C, consistent with the presence of a greater proportion of lipids with longer, more saturated fatty acid chains associated with the Lo (liquid-ordered) phase. It was concluded that the preparation of detergent-resistant membranes at 37 °C using buffer containing cations abundant in the cytoplasm might more accurately reflect the composition of lipid rafts present in the plasma membrane under physiological conditions.

Field-theoretical Renormalization-Group approach to critical dynamics of crosslinked polymer blends

We consider a crosslinked polymer blend that may undergo a microphase separation. When the temperature is changed from an initial value towards a final one very close to the spinodal point, the mixture is out equilibrium. The aim is the study of dynamics at a given time t, before the system reaches its final equilibrium state. The dynamics is investigated through the structure factor, S(q, t), which is a function of the wave vector q, temperature T, time t, and reticulation dose D. To determine the phase behavior of this dynamic structure factor, we start from a generalized Langevin equation (model C) solved by the time composition fluctuation. Beside the standard de Gennes Hamiltonian, this equation incorporates a Gaussian local noise, zeta. First, by averaging over zeta, we get an effective Hamiltonian. Second, we renormalize this dynamic field theory and write a Renormalization-Group equation for the dynamic structure factor. Third, solving this equation yields the behavior of S(q, t), in space of relevant parameters. As result, S(q, t) depends on three kinds of lengths, which are the wavelength q(-1), a time length scale R(t) approximately t(1/z), and the mesh size xi*. The scale R(t) is interpreted as the size of growing microdomains at time t. When R(t) becomes of the order of xi*, the dynamics is stopped. The final time, t*, then scales as t* approximately xi*z, with the dynamic exponent z = 6-eta. Here, eta is the usual Ising critical exponent. Since the final size of microdomains xi* is very small (few nanometers), the dynamics is of short time. Finally, all these results we obtained from renormalization theory are compared to those we stated in some recent work using a scaling argument.

Shaping Signals

Although keeping up with them can present difficulty for some human brains, it is evident that there are not enough distinct signaling mechanisms to account for the elaborate range of regulatory events that are controlled in a living organism. Neves et al. show one way in which fine-tuning of the same signaling pathway can allow distinct patterns of control. They examined the way in which cell shape impacts a classical signaling pathway from the β-adrenergic receptor through the second messenger adenosine 3′,5′-monophosphate (cAMP) to activation of mitogen-activated protein kinases (MAPKs) in neurons. Neves et al. used a combination of mathematical modeling of the system with measurements of temporal and spatial dynamics of signaling in isolated mouse hippocampal neurons with fluorescence resonance energy transfer imaging techniques. Their results show that the presence of adenylate cyclase activated by β-adrenergic receptors at the cell surface, with phosphodiesterase activity (which degrades cAMP) in the cytosol, along with other properties of the system, led to activation of gradients of signaling through cAMP to MAPKs. Furthermore, in part because the surface-to-volume ratio is very different in the narrow dendrites of a neuron compared with that in the neuronal cell body, there was a distinctly stronger signal in the dendrites than in the cell body, even though receptors are evenly distributed on the surface of the cell. Modeling indicated that the negative regulators would be key factors in controlling the size of microdomains of activation and propagation of spatially distinct signals through the pathway, and experimental manipulations verified this, with pharmacological inhibition of phosphodiesterase 4 allowing MAP kinase activation in the cell body as well as the dendrites. Kholodenko and Kolch provide commentary. S. R. Neves, P. Tsokas, A. Sarkar, E. A. Grace, P. Rangamani, S. M. Taubenfeld, C. M. Alberini, J. C. Schaff, R. D. Blitzer, I. I. Moraru, R. Iyengar, Cell shape and negative links in regulatory motifs together control spatial information flow in signaling networks. Cell 133 , 666-680 (2008). [PubMed] B. N. Kholodenko, W. Kolch, Giving space to cell signaling. Cell 133 , 566-567 (2008). [PubMed]

Cell Shape and Negative Links in Regulatory Motifs Together Control Spatial Information Flow in Signaling Networks

The role of cell size and shape in controlling local intracellular signaling reactions, and how this spatial information originates and is propagated, is not well understood. We have used partial differential equations to model the flow of spatial information from the beta-adrenergic receptor to MAPK1,2 through the cAMP/PKA/B-Raf/MAPK1,2 network in neurons using real geometries. The numerical simulations indicated that cell shape controls the dynamics of local biochemical activity of signal-modulated negative regulators, such as phosphodiesterases and protein phosphatases within regulatory loops to determine the size of microdomains of activated signaling components. The model prediction that negative regulators control the flow of spatial information to downstream components was verified experimentally in rat hippocampal slices. These results suggest a mechanism by which cellular geometry, the presence of regulatory loops with negative regulators, and key reaction rates all together control spatial information transfer and microdomain characteristics within cells.

Lipid Microdomain Formation: Characterization by Infrared Spectroscopy and Ultrasonic Velocimetry

We demonstrate the use of vibrational infrared spectroscopy applied to characterize lipid microdomain sizes derived from a model raft-like system consisting of nonhydroxy galactocerebroside, cholesterol, and dipalmitoylphosphatidylcholine components. The resulting spectroscopic correlation field components of the lipid acyl chain CH2 methylene deformation modes, observed when lipid multilamellar assemblies are rapidly frozen from the liquid crystalline state to the gel phase, indicate the existence of lipid microdomains on a scale of several nanometers. The addition of cholesterol disrupts the glycosphingolipid selectively but perturbs the di-saturated chain phospholipid matrix. Complementary acoustic velocimetry measurements indicate that the microdomain formation decreases the total volume adiabatic compressibilities of the multilamellar vesicle assemblies. The addition of cholesterol, however, disrupts the galactocerebroside domains, resulting in a slight increase in the lipid assemblies’ total adiabatic compressibility. The combination of these two physical approaches offers new insight into microdomain formation and their properties in model bilayer systems.

Characterization of the Ternary Mixture of Sphingomyelin, POPC, and Cholesterol: Support for an Inhomogeneous Lipid Distribution at High Temperatures

A ternary lipid mixture of palmitoyl-oleoyl-phosphatidylcholine (POPC), palmitoyl-erythro-sphingosylphosphorylcholine (PSM), and cholesterol at a mixing ratio of 37.5:37.5:25mol/mol/mol was characterized using fluorescence microscopy, 2H NMR, and electron paramagnetic resonance spectroscopy. The synthetic PSM provides an excellent molecule for studying the molecular properties of raft phases. It shows a narrow phase transition at a temperature of 311K and is commercially available with a perdeuterated sn-2 chain. Fluorescence microscopy shows that large inhomogeneities in the mixed membranes are observed in the coexistence region of liquid-ordered and liquid-disordered lipid phases. Above 310K, no optically detectable phase separation was shown. Upon decrease in temperature, a redistribution of the cholesterol into large liquid-ordered PSM/cholesterol domains and depletion of cholesterol from liquid-disordered POPC domains was observed by 2H NMR and electron paramagnetic resonance experiments. However, there is no complete segregation of the cholesterol into the liquid-ordered phase and also POPC-rich domains contain the sterol in the phase coexistence region. We further compared order parameters and packing properties of deuterated PSM or POPC in the raft mixture at 313K, i.e., in the liquid crystalline phase state. PSM shows significantly larger 2H NMR order parameters in the raft phase than POPC. This can be explained by an inhomogeneous interaction of cholesterol between the lipid species and the mutual influence of the phospholipids on each other. These observations point toward an inhomogeneous distribution of the lipids also in the liquid crystalline phase at 313K. From the prerequisite that order parameters are identical in a completely homogeneously mixed membrane, we can determine a minimal microdomain size of 45–70nm in PSM/POPC/cholesterol mixtures above the main phase transition of all lipids.

Characterizing the interactions between GPI-anchored alkaline phosphatases and membrane domains by AFM

In plasma membranes, most glycosylphosphatidylinositol-anchored proteins (GPI proteins) would be associated with ordered microdomains enriched in sphingolipids and cholesterol. Debates on the composition and the nano- or mesoscales organization of these membrane domains are still opened. This complexity of biomembranes explains the use, in the recent years, of both model systems and atomic force microscopy (AFM) approaches to better characterize GPI proteins/membranes interactions. So far, the studies have mainly been focused on alkaline phosphatases of intestinal (BIAP) or placental (PLAP) origins reconstituted in model systems. The data show that GPI-anchored alkaline phosphatases (AP-GPI) molecules inserted in supported membranes can be easily imaged by AFM, in physiological buffer. They are generally observed in the most ordered domains of model membranes under phase separation, i.e. presenting both fluid and ordered domains. This direct access to the membrane structure at a mesoscopic scale allows establishing the GPI protein induced changes in microdomains size. It provides direct evidence for the temperature-dependent distribution of a GPI protein between fluid and ordered membrane domains. Origins of reported differences in the behavior of BIAP and PLAP are discussed. Finally, advantages and limits of AFM in the study of GPI proteins/membrane domains interactions are presented in this review.

Docosahexaenoic acid alters the size and distribution of cell surface microdomains

We recently generated nutritional data suggesting that chemoprotective dietary n-3 polyunsaturated fatty acids (n-3 PUFA) are capable of displacing acylated proteins from lipid raft microdomains in vivo [D.W. Ma, J. Seo, L.A. Davidson, E.S. Callaway, Y.Y. Fan, J.R. Lupton, R.S. Chapkin, n-3 PUFA alter caveolae lipid composition and resident protein localization in mouse colon, FASEB J. 18 (2004) 1040–1042; Y.Y. Fan, L.H. Ly, R. Barhoumi, D.N. McMurray, R.S. Chapkin, Dietary docosahexaenoic acid suppresses T cell protein kinase Cθ lipid raft recruitment and IL-2 recruitment, J. Immunol. 173 (2004) 6151–6160]. A primary source of very long chain n-3 PUFA in the diet is derived from fish enriched with docosahexaenoic acid (DHA, 22:6n-3). In this study, we sought to determine the effect of DHA on cell surface microdomain organization in situ. Using immuno-gold electron microscopy of plasma membrane sheets coupled with spatial point analysis of validated microdomain markers, morphologically featureless microdomains were visualized in HeLa cells at high resolution. Clustering of probes within cholesterol-dependent (GFP-tH) versus cholesterol-independent (GFP-tK) nanoclusters was differentially sensitive to n-3 PUFA treatment of cells. Univariate K-function analysis of GFP-tH (5 nm gold) revealed a significant increase in clustering ( p < 0.05) by pre-treatment with DHA and linoleic acid (LA, 18:2 Δ9,12) compared to control fatty acids; whereas LA significantly ( p < 0.05) reduced GFP-tK clustering. These novel data suggest that the plasma membrane organization of inner leaflets is fundamentally altered by PUFA-enrichment. We speculate that our findings may help define a new paradigm to better understand the complexity of n-3 PUFA modulation of signaling networks.

Design of nanostructured ceria-based solid electrolytes for development of IT-SOFC

A considerable interest has been shown in the application of doped ceria (CeO2) compounds for “intermediate” (300–500 °C) temperature operation of solid oxide fuel cells. The microdomains with ordered structure of oxygen vacancy were observed in the microstructure of the M-doped CeO2-sintered bodies (where M: Gd, Y, and Dy). We have previously shown that the conductivity of doped CeO2-sintered bodies was lower when the sintered body contained large microdomains within grains. As a consequence of this observation, we have examined the grain size dependence and dopant content on conductivity in specimens where we adjust the microdomain size and a degree of oxygen vacancy ordering in the microdomains by controlling the microstructure. The microdomain size control in Dy-doped CeO2 specimens was obtained by combining pulsed electric current sintering and conventional sintering. Using these techniques, we were able to improve the conductivity in Dy-doped CeO2 specimens to a point where it became comparable to that of the more conventional Gd-doped CeO2 specimens. It is concluded that by combining ultimate high-resolution analysis of these nanostructures with the adjusting processing route design, it is possible to further develop these materials in CeO2-doped fuel cell application.

Orientationally Controlled Nanoporous Cylindrical Domains in Polystyrene-b-poly(ferrocenylethylmethylsilane) Block Copolymer Films

The self-assembly of thin films of organometallic cylinder-forming amorphous polystyrene-block-polyferrocenylsilane diblock copolymers is described. By varying film thickness and/or the conditions of toluene during evaporation annealing, well-ordered arrays of hexagonally packed iron-rich cylindrical microdomains oriented either parallel to or normal to the substrate were produced. In the latter case, when the film thickness was very small (12−15 nm), well-defined nanoporous cylindrical domains were found. This unique morphology persists in UV ozone etched films where inorganic, ring-like cylindrical domains were produced. By varying the rate of solvent evaporation from solvent-swollen films, control over the orientation, order, and size of the cylindrical microdomains was achieved and variation of the fundamental morphology was observed.